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taric acid, in many plants. It is prepared principally from
lemon juice, from \vhich it. is precipitated as the calcium salt on
boiling with chalk and also l>y the citric fermentation of

Properties.—The acid, which contains I molecule of water,
crystallises in prisms ; soluble in water, alcohol, and also mo-
derately soluble in ether ; m. p. 100°. The anhydrous acid melts

at 153—154°.                     .              '

Reactions.— i. Meat a little of the acid and notice the irri-
tating vapours.

Make a neutral solution of sodium citrate by adding caustic
soda to a solution of the acid.

2.  Add lime water. There is no precipitate of the calcium salt,
(C(.JIrp7)Xa.{4-4H/>, until the solution is boiled.

3.  Add calcium chloride solution and boil, and, to another
portion, silver nitrate solution.     Note the results and compare
the reactions with those of tartaric acid (p. 115),

Citraconic and Mesaconic Acid.
(Methyl fumarlc and Methyl maleic acid).
Kekule, Lchrbiich, 2, 319; Kittig, Anualcn^ 1877, 188, 73.
250 grms. citric acid (crystallised).
Heat the crystallised citric acid, without powdering, in a porce-
lain basin to a temperature not exceeding 150°. The water of
crystallisation is expelled, and the crystals become pasty and
then fluid. When cold, the solid mass is removed from the
basin by gently wanning, and is coarsely powdered. The anhy-
drous acid is rapidly distilled in portions of 100 grams, from a
retort (250 c.c.) with bent neck (sec Fig. 19, p. 22), fitted to a con-
denser, the receiver being a separating funnel. The distillate
consists of two layers. The lower layer of impure citraconic
anhydride is run off, and. the upper layer, consisting of water and
citraconic acid, is fractionated, the portion distilling at 190—210°
being collected and mixed with the previous lower layer.